The central assumption governing the design and operation of all major
water projects has just been declared dead by a group of leading water
and climate scientists. Designers and builders of dams need take note.
The
scientists, led by Paul Milly of the US Geological Service, explained
in a recent article in Science that our dams, floodwalls and sewers
have been designed and operated under the assumption of "stationarity"
- that natural systems fluctuate within a defined set of extremes that
can be estimated from past experience. But climate change means
"stationarity is dead" for water resources planning, the scientists say.
Two
recent studies of the western US from scientists at the University of
California's Scripps Institute show just how quickly streamflow is
changing. One study found declining snowpacks and earlier spring river
run-off over the past 50 years, all consistent with climatologists'
models. The authors maintain that models for future warming mean "a
coming crisis in water supply" over the next 20 years for an already
water-stressed region."
A second study's findings were
shocking even to longtime observers of US water resources. This study
calculates that Lake Mead, the massive desert reservoir behind Hoover
Dam, could run dry within 13 years if climate changes as predicted.
There is only a 50% chance of there being enough water in the Colorado
River within nine years to turn the turbines at Hoover. "We were
stunned at the magnitude of the problem and how fast it was coming at
us," the lead author told journalists. Lake Mead supplies almost all
the water for Las Vegas and much of that used in southern California
and Arizona.
The inability of water planners to cope with the
new paradigm imposed by global warming is strikingly shown by a study
on allocating Colorado River water in dry years, released last year by
the Bureau of Reclamation. . . Although the issue under consideration
was how to deal with hydrological extremes, the Bureau's study did not
look at the impacts of climate change.
This head-in-the-sand
approach unfortunately appears to be the rule in dam planning. While
dam feasibility studies are now finally starting to mention the impacts
of climate change, the norm seems to be that they do so only to dismiss
them.
The recent economic study by Power Planning Associates
Ltd. used to help justify the World Bank's approval of Bujagali Dam in
Uganda dismisses the possibility of climate change altering flows of
the Nile out of Lake Victoria (the source for Bujagali). "[C]limate
change is not found to be significant enough in the medium term [to
2030] to influence hydrological scenarios" for this dam, say the
consultants. Even more mind-boggling is the complete denial of the
impacts of global warming in last year's environmental study for
Ghana's Bui Dam by consultancy ERM. This claims that climate change
will only affect dam safety and performance "over the very long term
(i.e., thousands of years)."
To be fair to the consultants,
there is as yet no agreed concept to replace stationarity. And it is
never easy for professionals to discard the assumptions on which their
training and careers have been based. Paul Milly and his colleagues
suggest a framework for post-stationarity water resources planning, and
it is clear that this must be based on broadening the range of
potential flow scenarios and helping decision-makers understand the
implications of increasing hydrological uncertainties.
But just
pretending that climate is not changing, and encouraging governments to
make major investments in climate-sensitive infrastructure on this
basis is highly irresponsible. The government of the Caribbean nation
of St. Vincent and the Grenadines noted in the UN General Assembly on
February 13 that "[m]any of us are still paying for infrastructural
investments that are no longer viable, or whose effective lifespan will
be severely curtailed by climate change. Many of us have to borrow more
to retrofit previous investments, which are often funded and designed
and built by foreign lenders. It is illogical and immoral that we
continue to pay developed creditor states for items whose very use is
compromised by their actions."
If such calls for
accountability become more common, water resource consultants may
finally have to face a harsher climate reality.
